Prairiedawg

Friday, I took the 911 to a local Indy and had fresh Pilot Sport 4S tires installed. All 4 tires plus an alignment was done. Picked up the car and drove it slowly through rush hour traffic to an event Friday evening on unfamiliar roads. I drove the car home afterwards through road construction then mostly highway driving the way back. The way home, I couldn't help but think I feel a slight vibration the entire time above 70 mph and possibly slower. The car was out of alignment before and the tires had improper wear that indicated that. I never gave it much thought because the tires were old, hard and had alignment wear. Plus it's a 911 with the suspension that comes with it and hydraulic steering etc.

To me, it actually feels worse than it did before. I don't want to be hyper sensitive and feel like there's something there that isn't or is and should be because it's a sports car, not a Cadillac. Some caveats here. One, the roads here are terrible, especially for evaluating a vibration. I drove home almost entirely on unfamiliar roads on concrete highway which has a rough groovy surface for traction in slippery conditions. That's how they do that here. I'm trying to think where we have fresh asphalt nearby where I can get up to speed for a sustained period to evaluate things. Nothing comes to mind. also, the vibration doesn't seem to be in the steering which makes me think it would be in the back axle.

Some questions for the smart people here. The tires have less than 50 miles on them, do they need to break in and would that give me a sensation that should go away? Do you see anything in the alignment report that could cause a difference in feeling? Do these cars just do that, and I'm experiencing something that has always been there and I'm expecting too much with new tires on a sports car? The thing that stood out to me was it was very slight but noticeable to me over 70mph. It didn't matter which lane I chose, it was consistent. The car seemed to drive true and would pull left or right, depending on which side of the crowned highway lane I was in. The tires were installed by a Euro Indy and Roadforce balanced on a Hunter machine. Is it just an off balance job and or something else there possibly, or all in my head? Any tips for evaluating before I call the Indy to have them investigate are appreciated.


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ajayabb

I wonder if you could have lost a balancing weight on the drive leaving with a unbalanced tire in the rear. Also there is a layer on new tires that facilitate new tires release from the molds during production that will give you a slippery feel when new for a couple hundred miles.

Prairiedawg

No slippery feeling. Not pushing the car at all, just straight down the highway. I will say, the car had been running like crap that day. Rough idle, etc. I think I got a batch of sub-optimal gas when I filled up last sunday and drove home. I didn't notice anything that day, just friday morning when I started it up and the idle had been very rough. I think to two are disconnected though, yes it's running like crap but the vibration is at higher speeds. I have a Foxwell I can connect and look at the DME but wouldn't know what I'm looking at. We may explore that too.

MarkinMD

I have had the same situation a few times over the years. Re-balancing the tires always cleared it up. A tire could have slipped slightly on the rim, or as @ajayabb suggested, a weight could have fallen off. Ask your Indy to check the balance. In the meantime, you could double check that all the lug nuts are properly torqued.

Ironman88

Just a few thoughts:

1) There's a good chance that the tire balance has not been done well - and if you're not feeling it in the steering (but maybe through the "seat of your pants" so to speak, it probably is one of the rear tires (or both maybe).
2) Are you running wheel spacers? If so, maybe one (or more) are not seated properly.
3) May want to reconfirm that your tire pressures are set properly all around

4) Regarding the rough idle - you may want to consider using Sta-Bil 360. Added when you fill the tank. 1 ounce per 5 gallons of gas. It contains PEA (Polyetheramine) which is an excellent cleaner for injectors as well as the complete fuel system Sta-Bil 360 will also aggressively address any water in your tank or fuel system - which is almost guaranteed as being an issue given the use of ethanol-based fuels.

GTSpure

Agree about wheel alignment.
In 997 wheel alignment is not simple.
Sometimes it takes more than once to achieve a perfect result. 997 is also very sensitive to the road.Check on a smooth road, the reason may be the road and not the Porsche. If there is a section that you check and there are no vibrations and there is another section that has vibrations, that is the road.

Regarding the idle, an interesting point, what is the difference between the Sta-Bil 360 fuel additive and the original Porsche fuel additive?
BTW, in the user's car book, Porsche specifically stated that it does not recommend fuel or oil additives. I have not yet found a clear answer to the issue.
In addition, it is important to note that if you use a fuel additive, I think you should use it before changing the oil.

NevilleNobody

Need clarification. Is it a pull or a vibration? My understanding, correct me if I am wrong, is a vibration is likely to be balancing and a pull the alignment.

anewman

Make sure all lug nuts are tight. One wheel could have not seated properly when mounted, and the drive home could have moved it slightly and left loose lug nuts and a wobbly wheel. Once you’ve check that, drive it back the the tire shop and have them rebalanced them. 99% that will resolve the issue.

Prairiedawg

A few clarifications. First is no lug nuts, centerlocks. hopefully they are installed correctly. I have to assume so. Second is it's not pulling. It drives straight as far as I can tell. I should have left that out as it only adds to confusion. Third is the rough idle. I just drove the car last Sunday for the first time since it came out of storage. At that time, it had a full tank of non-ethanol gas with Sta-bil added at the time of storage. Every year I drive the last tank of gas through with Techron etc. and then have the oil changed, filled with gas, stabil added, goes into storage. It ran fine all day last Sunday and needed gas to get home. I filled the tank and drove about an hour home with more non ethanol gas from a BP station in southern Wisconsin. Parked it until Friday morning when I took it for the tire replacement. Friday morning it ran like crap and did so all day. I have to assume I have a bad batch of gas and it will clear with an empty tank.

My plan today is to take my Boxster out and fine a long smooth patch of pavement and set a benchmark. I'll then take the 911 and drive the same stretch of road at similar speeds and see if I can compare the two. In the end though, it's probably a bad balance job which will be aggravating since I'll have to take a day off of work to get rectified if that's the problem.

Ripking

Take it back and have the wheels balanced. It’s only happening at a certain speed. It’s almost certainly out of balance. If it’s not that I would be shocked.

groovzilla

Only vibration I've encountered was related to subpar Spacers. Are you using Spacers on your wheels?

GTSpure

I understand you. It's very frustrating. It is also very difficult to balance our Center Lock... and Not everyone has the right equipment. (recommended to balance with Hunter Road Force.) Good luck friend

Sporty

Ask when their machine was last calibrated and be there with the Tech as he walks you thru each step, checking for out of round, matching high spots to low spots rim and tire. Also, sometimes they balance/ to an "acceptable " tolerance level which is not really good enough for these cars - want to get as close to zero as possible. In addition to all the other comments, this advice is super meaningful and easiest to go through - you should follow up with it. Ask me how I know .....

Mike Murphy

If a rebalance doesn’t fix it, and a road-force balance doesn’t fix it, you might have a bent rim that’s nearly impossible to tell by looking at it. I also agree with the spacers comments.

Prairiedawg

Ok, took both cars for a ride on a long straight smooth country road. The 911 definitely has a little shimmy at speed. The Boxster runs nice and smoothly as expected. Starts to be noticeable over 60 mph but unmistakable past 80. At speed in gear or in neutral made no difference. Not major and life threatening but vibrates worse than it did with the tires that were just replaced. The tires were Road Force balanced. I suspect, like noted above, were balanced good enough. Just not good enough for a high spec sports car. I'll call them tomorrow and let them know there's a problem.

Centerlock wheels, no spacers. I don't think there's a bent wheel, I noticed nothing on the way to get tires, only on the way home.